JP2895330B2 - Gamma ray measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the level, density, thickness, etc. of a liquid in a non-contact manner, for example, in a flammable chemical or a plant requiring explosion-proof performance, or in a bad environment such as a high temperature. The present invention relates to a gamma ray measuring device.

[0002]

2. Description of the Related Art There are gamma ray measuring devices such as a level meter, a density meter, and a thickness meter that use gamma rays. In this gamma ray measuring device, a change in a physical quantity is measured using attenuation of a gamma ray emitted from a gamma ray source. The attenuated gamma rays are detected by a gamma ray detector combined with an ionization chamber or a scintillator and a photomultiplier tube. And
The detected gamma ray is converted into an electric signal and can be measured as a change in a physical quantity. At present, generally used gamma ray detectors are a combination of a scintillator and a photomultiplier tube. As the scintillator, liquids and solids are often used, and in particular, sodium iodide (containing thallium) or cesium iodide (containing thallium) in which thallium is mixed with an alkali metal salt, and the amount used is large. In recent years, a plastic scintillator in which thallium is mixed with plastic is sometimes used for high-precision measurement or a large detector.

An example of the gamma ray measuring device is disclosed in Japanese Patent Application Laid-Open No. 2-74827. FIG.
FIG. 2 is a schematic configuration diagram of the gamma ray measuring device. FIG.
In the above, the liquid 2 is stored in the container 1, and the level of the liquid 2 changes according to the operating condition of the plant. On one side of the container 1, there is a gamma ray source 4 such as cobalt or cesium contained in the source container 3, and irradiates the container 1 at an angle indicated by θ. On the other side of the container 1, a plastic scintillator 5 and a photomultiplier tube 6 are provided.
16 (indicated by a dashed line), and the respective positions of the detectors 7 in the vertical direction in FIG. 16 are often shown in the figure. The gamma ray source 4 may be arranged near the center of the container 1 depending on the shape of the container 1 or the like.

[0004] A light guide 8 is provided between the plastic scintillator 5 (hereinafter abbreviated as "plasin 5") and the photomultiplier tube 6, and emits light for several tens to several hundreds of nanoseconds (ns) when the plasticine 5 emits light by gamma ray irradiation. The light pulse is configured to be efficiently transmitted to the photomultiplier tube 6.
A light pulsar 9 is optically coupled and incorporated near the contact surface between the plasticine 5 and the light guide 8. The light pulsar 9 has a small amount of sodium iodide scintillator and a small amount of source, and is americium (Am energy 3.
4MeV) to generate a very strong light pulse. Americium sources have a long half-life of 433 years. Therefore, the americium source is a stable light source for a long period of time. The optical pulse signal from the detector 7 having such a configuration is supplied to an amplifier (amplifier) 10 and amplified.

FIG. 17 is a graph showing an example in which the output signal of the amplifier 10 is analyzed by a multi-channel pulse height analyzer. In FIG. 17, the horizontal axis represents the pulse height PH of the optical pulse signal.
(Pulse height), and the vertical axis is the number N of optical pulses at each wave height. There are two crest distribution groups in the figure,
Wave height B and below. The light pulse having a wave height of B or less is a level signal of plasin light generated when gamma rays emitted from a gamma ray source such as cobalt or cesium are attenuated by a measurement object and incident on plasin. Therefore, in this wave height distribution group, the number of light pulses changes according to the liquid level in the container 1. A group of light pulses having a wave height B or more is caused by the light pulser 9. Light pulsar 9
Light has an energy of 3.4 MeV, which is about 2.
Because it is five times larger, the wave height is higher than that of cobalt or cesium. Further, since the scintillator uses an inorganic substance of sodium iodide, the wave height distribution also has a relatively narrow Gaussian distribution, and does not mix with the level signal. Using the optical signal of the light pulser 9, the amplification degree of the measurement system is automatically corrected so as to eliminate the influence of the disturbance of the measurement system and the change with time described below, thereby realizing stable measurement.

That is, in FIG. 17, the optical pulse output of the amplifier 10 is separated by two comparators 11 and 13. The first comparator 11 sets the comparison reference wave height to the value of C in FIG. 17, passes a wave height signal equal to or higher than the noise component, and the arithmetic unit 12 converts the number of pulses into a level signal, and
Output. The second comparator 13 sets the comparison reference wave height as the center wave height value A of the light pulse group by the light pulser 9. Then, only the light pulse having a wave height larger than A is passed, and the number of pulses set in advance by the arithmetic unit 14 and the number of pulses passed through the second comparator 13 (that is, the number of pulses indicated by oblique lines in FIG. 17) Is compared. Further, the arithmetic unit 14 controls the voltage applied to the photomultiplier tube 6 so that the difference from the set value is eliminated.
ge) Supply a signal to the control circuit 16. The high voltage power supply 15
According to the signal from the HV control circuit 16, the photomultiplier tube 6
A high voltage is applied to.

The number of light pulses emitted from the light pulser 9 is as follows:
Since the half-life of the α-ray source is as long as 433 years, it is very stable. Therefore, as described above, the second comparator 1
3 so that the number of pulses passing through 3 becomes constant.
By controlling 5, the amplification degree of the optical pulse measurement system including the level signal can be kept constant. For example, a change in the amplification degree depending on the temperature of the photomultiplier tube 6 (about -0.2 to -0.0.
4% / degree C), change in amplification due to aging, plus 5
Even if there is a change in the light transmittance inside and a change in the temperature of the amplification degree of the amplifier 10, the amplification degree of the photomultiplier tube 6 can be corrected by changing the output voltage of the high-voltage power supply 15 as a whole, and the level can be stabilized. Can be measured.

[0008]

However, in the above conventional gamma ray measuring apparatus, the stability of the measuring system is as follows.
Very good around room temperature, but ambient temperature is -10
When the temperature greatly changes to 50 ° C., the luminous ability of sodium iodide, which is a scintillator used in the light pulser 9, changes, and the wave height of the luminescence pulse changes. Therefore, the measurement accuracy has deteriorated.

Americium, which is an α-ray radiation source, has statistical noise peculiar to atomic decay. To improve the instrument accuracy, use a source with a large amount of radiation or use for several tens of minutes. However, there is a problem that the measurement time is lengthened.

Further, a radiation source of α rays is used as the light pulser 9.
Due to the difficulty, it was necessary to manage not only the gamma ray source but also the α ray source, and a great deal of cost and labor had to be spent on the management.

The pulse height of the light pulser 9 is fixed and cannot be changed to a desired value. For example, when the measurement object changes from a low density to a high density, the radiant energy of the gamma ray source is small, for example,
It is necessary to switch from cesium to cobalt, which has high radiant energy. In this case, since the pulse height of the α-ray source is fixed, the peak level of cobalt and the peak level of the α-ray source overlap. Therefore, it is difficult to clearly separate the pulse of the gamma-ray source from the pulse of the α-ray source, and the measurement accuracy is reduced.

An object of the present invention is to provide a gamma ray measuring apparatus which is less affected by changes in ambient temperature and statistical noise, is easy to manage, can accurately cope with changes in the object to be measured, and has improved measurement accuracy. is there.

[0013]

Means for Solving the Problems (1) The present invention is configured as follows to achieve the above object. That is ,
In a gamma ray measuring device, a pulse signal generating means capable of adjusting an output pulse width, and an optical pulse having a pulse width different from a pulse width of a pulse signal generated from a gamma ray source based on a pulse signal from the pulse signal generating means. A reference light generating means for generating a signal, and changing the wave height of the pulse signal generated from the pulse signal generating means in accordance with a change in the ambient temperature, thereby obtaining a light emission amount of the optical pulse signal generated from the reference light generating means. And a temperature compensating means for making the amount substantially constant irrespective of a change in the ambient temperature, and a pulse number of a pulse signal from the reference light generating means supplied via the photoelectric conversion means so that the pulse number becomes a predetermined value. , and a voltage control means for varying the supply voltage to the photoelectric conversion means.

(2) In the gamma ray measuring device,
A pulse signal generating means capable of adjusting the crest level of the output pulse signal; and an optical pulse signal having a crest level different from the crest level of the pulse signal generated from the gamma ray source, based on the pulse signal from the pulse signal generating means. The reference light generating means and the pulse height of the pulse signal generated from the pulse signal generating means are changed in accordance with a change in the ambient temperature, and the light emission amount of the light pulse signal generated from the reference light generating means is changed. Temperature compensating means for making the amount substantially constant irrespective of a change in temperature, and the pulse number of the pulse signal from the reference light generating means, which is supplied via the photoelectric conversion means, has a predetermined value. and a voltage control means for varying the supply voltage to the photoelectric conversion means.

(3) In the gamma ray measuring device,
Pulse signal generating means having a constant number of output pulses, reference light generating means for generating a light pulse signal having a predetermined number of pulses based on the pulse signal from the pulse signal generating means, Temperature compensating means for changing the wave height of the pulse signal to be generated in accordance with a change in the ambient temperature, so that the light emission amount of the optical pulse signal generated from the reference light generating means is substantially constant regardless of the change in the ambient temperature. Voltage control means for changing the supply voltage to the photoelectric conversion means so that the number of pulses of the pulse signal from the reference light generation means becomes a predetermined value, supplied through the photoelectric conversion means ; equipped with a.

(4) Preferably, the above (1), (2),
In (3), the reference light generating means includes a light emitting diode.
Pulse signal supplied to the light emitting diode.
The pulse width of the light emitting diode is 1 to 10 μs.
The emission wavelength of the laser is 400 to 600 nm, or
Generated from the light emitting diode through the photoelectric conversion means
The counting rate of the pulse signal
The count rate of the pulse signal generated via the conversion means is set to 0.
5% to 10%. (5) Preferably, the above (1), (2), (3)
Wherein the signal from the photoelectric conversion means is amplified.
From the amplifier and the output signal from the amplifier to the gamma ray source
A first comparator for extracting a signal based on the first
Based on the signal extracted by the comparator,
A first computing unit for computing the level, density, etc. of the
Gamma-ray source based signal and reference
A time constant circuit for separating the signal based on the light generating means;
From the output signal from the serial time constant circuit, a reference light generation means based on
And a second comparator for extracting the following signal.
The number of pulses of the signal extracted by the parator and a predetermined number
Comparing and calculating a difference between the number of pulses and a predetermined number.
A high-voltage unit for supplying a high voltage to the arithmetic unit and the photoelectric conversion unit.
A power supply, wherein the voltage control means includes a second operation
The output voltage of the high-voltage power supply according to the output signal of the
You. (6) Preferably, in the above (5), the MV is
The control signal, PB is the proportional band, Pin is the second comparator
All the number of pulses of output signal and Pr are generated from the reference light generator
When the number of pulses, PS is the reference ratio of Pin and Pr, and Ti is integrated
If it is between, the second computing unit calculates MV = (1 / PB) (P
PI control represented by S− (Pin / Pr)) / (Ti + 1)
Executes the operation and supplies the control signal MV to the voltage control means.
I do. (7) Preferably, the above (1), (2), (3)
Wherein the reference light generating means is a light emitting diode,
This light emitting diode has a light emitting wavelength in one package.
Include two light emitting diode elements different from each other. (8) Preferably, in (7) above,
From the pulse signal output from the pulse signal generation means
Generates two types of pulse signals with alternate generation timing
And a pulse signal dividing means for generating the pulse signal.
The above two types of pulse signals are supplied to the light emitting diode element
And emit light substantially alternately. (9) Preferably, in the above (6), the ratio Pin
/ Pr is 0.02 ≦ Pin / Pr ≦ 0.2, and 0.8
≤ Pin / Pr ≤ 0.98. (10) Also, preferably, the above (1), (2),
In (3), at least the photoelectric conversion means and the pallet
Signal generation means, temperature compensation means, voltage control means,
The reference light generator is housed in a flameproof structure case.
This explosion-proof case is made of plastic
And two independent light sources on this connection surface.
A passage is formed.

[0017]

The amount of light generated by the reference light generating means is temperature compensated by the temperature compensating means.
It is almost constant. The voltage control means adjusts the supply voltage to the photoelectric conversion means so that the number of pulses of the pulse signal from the reference light generation means has a predetermined value. Since the amount of light generated by the reference light generator is stable, the adjustment of the supply voltage by the voltage controller is performed with high accuracy. Therefore, the level, density, and the like of the measured object are accurately measured. In addition to the temperature-compensated reference light generating means, a light generating means whose amount of generated light changes according to a change in the ambient temperature may be arranged to detect the state of the ambient temperature.

[0018]

FIG. 1 is a schematic block diagram of a gamma ray measuring apparatus according to an embodiment of the present invention. The difference between the example of FIG. 1 and the conventional example of FIG. 16 is that the light emitting diode 17 (reference light generating element) arranged near the lower portion of the plasticine 5, the pulse oscillator 18 for exciting the light emitting diode 17, and the ambient temperature are different. A temperature correction circuit 19 for controlling a current flowing through the light emitting diode 17 and a time constant circuit 20 are provided so that the amount of light emitted from the light emitting diode 17 is constant even if the light emission changes. In FIG. 1, the pulse width and pulse height of the pulse oscillator 18 are adjustable. The pulse signal from the pulse oscillator 18 is supplied to the light emitting diode 17 via the temperature compensation circuit 19. Then, the light emitting diode 17 emits light according to the supplied pulse signal. The light generated from the light emitting diode 17 is detected by the detector 7.
The light is scattered and reflected in the inside and enters the plastic scintillator 5. Then, the light is further scattered and reflected in the scintillator 5, and is incident on the photomultiplier tube 6 together with the gamma-ray plasin light. Both optical signals (pulse widths different from each other) are amplified by the amplifier 10, and the pulse that has passed through the first comparator 11 is calculated by the calculator 12, becomes a normalized level signal, and is sent to a converter (not shown). Supplied.

On the other hand, both optical signals supplied to the time constant circuit 20 are attenuated by a CR circuit having a time constant of τ = CR, and the pulse height distribution changes from the distribution shown in FIG. As shown in the distribution, the light-emitting diode optical signal (shaded portion) and the plasin signal are separated. In order to separate light emitting diode light and plasin light more accurately,
A detector that performs synchronous detection with the excitation pulse of the light emitting diode may be provided in a stage preceding the second comparator 13.

The signal obtained by passing through the time constant circuit 20 is selected by the second comparator 13 from the comparison voltage VC2 shown in FIG. Then, in the arithmetic unit 14, the comparator 13
The PI control represented by the following equation (1) is performed so that the count value of the light-emitting diode optical signal that has passed through becomes constant, and a control signal is supplied to the HV control circuit 16. Then, the HV control circuit 16
Thus, the voltage supplied from the high voltage power supply 15 to the photomultiplier tube 6 is controlled. MV = (1 / PB) (PS− (Pin / Pr)) / (Ti + 1) (1) where MV is a control output, PB is a proportional band, and Pin is a light emitting diode that has passed through the second comparator 13. , Pr is the total number of pulses of the light emitting diode (excitation frequency),
PS is a reference value of the ratio between the pulse numbers Pin and Pr, and Ti is an integration time. The ratio Pin / Pr of Pin and Pr is 0.02
≦ Pin / Pr ≦ 0.2, 0.8 ≦ Pin / Pr ≦ 0.98

Generally, the amount of light emitted from the light emitting diode 17 as a semiconductor component is affected by the ambient temperature. However, the influence of the ambient temperature of the light emitting diode 17 can be sufficiently corrected. That is, since the light emission amount of the light emitting diode 17 changes at a rate of -0.3 to -0.5% / degree C at ambient temperature, the temperature of the light emitting diode 17 is detected so that the light emission amount becomes constant. Temperature compensation is required. FIG.
Is a circuit diagram showing an example of a temperature compensating circuit 19, in which a thermistor RT as a temperature-sensitive element and resistors R1 and R2 are used. In FIG. 2, the light emitting diode 17 has a resistor R
Connected to the power supply E via 1 and R2. Then, the thermistor RT is connected in parallel to the resistor R2. The temperature compensation circuit suppresses the amount of light emitted from the light emitting diode 17 from being affected by a temperature change.

FIG. 3 is a circuit diagram showing another example of the temperature compensation circuit 19, in which a transistor Tr is used. In FIG. 3, the light emitting diode 17 includes a transistor T
r, connected to the power supply E via the resistor RE. The base of the transistor Tr is connected to the resistor RE. The base-emitter voltage VBE of the transistor Tr has a negative temperature characteristic, and the current IF flowing through the light emitting diode 17 is represented by the following equation (2), where the base voltage is VB.

IF = (VB−VBE) / RE (2) In the above equation (2), when the ratio between the voltages VB and VBE is changed, the rate at which the current IF changes with temperature can be freely adjusted. Temperature compensation becomes possible. In addition, it is also possible to adopt a configuration in which the ambient temperature is detected by using a temperature measuring resistor or a thermocouple, and the current IF is changed in accordance with the detected temperature to perform the temperature compensation.

The response time of the light emitting diode 17 is 0.05
Since it is as short as 0.1 μs and responds satisfactorily at a high frequency of several MHz, it is possible to generate an optical pulse equivalent to that of the plasin light, and to easily change the pulse number and pulse shape. Further, the light emission intensity of the light emitting diode 17 is 1000 light of the light pulser 9.
Since the number is twice or more, there is an advantage that the light from the light emitting diode 17 can be indirectly incident through the outer wall of the plasticine 5. It is preferable to use a wavelength of the light emitting diode 17 of 400 to 600 nm (blue to green) in which the sensitivity of the photomultiplier tube 6 is good. FIG. 4 shows the results obtained by combining the light emitting diode 17 and the photomultiplier tube 6 and measuring their step responses. FIG. 4B shows a current waveform ID flowing through the light emitting diode 17, and FIG.
Indicates an output signal waveform So of the photomultiplier tube 6.

From the result shown in FIG.
Is short as described above, but the combined response time τ of the light emitting diode 17 and the photomultiplier tube 6 is about 0.5 μs, including the rise time of the current. The light from the light emitting diode 17 is composed of a DC component represented by A0 and AC random light having a width represented by B0. This AC random light has a pulse height similar to that of the plasin light emitted when gamma rays enter the plasin 5 and cause an error in level measurement. In one embodiment of the present invention, in order to minimize the error, the supply current to the light emitting diode 17 is set to a pulsed current ID as shown in FIG. ing. FIG. 5A shows an output signal of the photomultiplier tube 6. With the signal shown in FIG. 5, the light emitting diode signal can be handled as a pulsed light signal equivalent to the level signal. FIG.
In B1, B1 indicates the peak value of the current flowing through the light emitting diode 17, t1 indicates the excitation time, and t2 indicates the stop time.
Therefore, the excitation frequency f of the light emitting diode 17 is given by the following equation (3). f = 1 / (t1 + t2) (Hz) (3) FIGS. 6 and 7 show that the pulse current for exciting the light emitting diode 17 and the frequency are kept constant at 20 kHz, the ratio of the time t1 to t2 is changed, 3 shows the result of a light-emitting diode light incident on the photomultiplier tube 6 through which the output signal from the photomultiplier tube 6 was subjected to wave height analysis. The horizontal axis indicates the pulse height (PH), and the vertical axis indicates the number of pulses (N). The solid lines are the light emitting diode signals L1 and L2, and the dotted line is the signal S of the plasin light obtained by irradiating plasin 5 with gamma rays of cobalt.
Indicates P. The difference between FIG. 6 and FIG. 7 is an example in which the pulse width t1 is t1 = 20 μs in FIG. 6 and t1 = 2 μs in FIG. As can be seen from FIG. 6, when the pulse width is large, the AC random signal indicated by oblique lines is large, and the pulse height is substantially the same as that of the gamma ray level signal SP of cobalt.
Measurement accuracy is degraded. Further, since the height and sharpness of the reference pulse for stably controlling the high-voltage power supply 15 are poor, separation from the plasin light by the cobalt irradiation becomes inaccurate, and it is not possible to control the high-voltage power supply sufficiently stably.

On the other hand, in the case of FIG. 7 where the pulse width is small, the AC random signal indicated by oblique lines is extremely small, the height of the reference pulse is high, and the pulse height distribution is sharp. Therefore, it can be understood that the signal becomes higher and both signals can be completely separated. However,
It is not always better to make the pulse width smaller. If the pulse width of the excitation current of the light emitting diode 17 is 1 μs or less, the response time becomes 0.5 μs, so that sufficient light emission cannot be obtained. Therefore, the pulse width is 1 to 10
μs is optimal. Normally, in a level meter, the difference span between the zero point and the span point of the number of pulses of the gamma ray signal is several tens kc.
ps to several hundred kcps, but several kcps are used for level switches used to detect abnormal levels.
Sometimes used in spans. For this reason, the excitation frequency of the light emitting diode 17 is set to one of the pulse number of the
If the level is not set to 0% or less, of the level signals, a fixed component signal irrelevant to the level increases, which causes deterioration of measurement accuracy. On the other hand, if the frequency becomes too low, the noise resistance becomes poor, and if the frequency becomes 0.5% or less of the number of pulses of the gamma ray signal,
The minimum adjustment voltage of the HV control circuit 16 becomes too large to be practical. Therefore, the excitation frequency of the light emitting diode 17 is selected to be 0.5% to 10% of the pulse number of the gamma ray signal. Reference numeral 21 denotes a printed circuit board, on which the pulse oscillator 18, the amplifier 10, the arithmetic circuits 12, 13 and the like are arranged.

As described above, according to one embodiment of the present invention, the light emitting diode 17 is used as the reference light generating element, and the temperature compensating circuit 19 for compensating the change in the amount of light emitted from the light emitting diode 17 with the ambient temperature is provided. Placed. This makes it possible to realize a gamma ray measuring device that is less affected by changes in the ambient temperature and that is easy to manage. When a radiation source is used as the reference light generating element, statistical noise is generated as in the pulse number Nα shown in FIG. Due to this statistical noise, the number of pulses Nα is determined by the variation range σ = k / N ^0.5
Only fluctuates. Here, N is the number of pulses, and k is a constant. Usually, when the pulse number N is 1000 cps, the fluctuation width σ is about 1%, and when N is 100 cps, the fluctuation width σ is 2.5%.
% To 3.0%.

On the other hand, when the light emitting diode 17 is used as the reference light emitting element as in one embodiment of the present invention, the number of light emitting pulses of the light emitting diode 17 is set to the pulse number NL shown in FIG. Thus, it can be constant. Therefore, the detection of the reference light can be accurately performed in a short time, and a gamma measuring device with high control response can be executed.

Furthermore, since the pulse height of the pulse generated from the light emitting diode 17 can be adjusted, it is possible to cope with a change in the gamma ray source accompanying a change in the object to be measured. That is, the energy of the gamma ray source is cobalt ⁶⁰ Co (dashed line) is 1.17 or 1.33 MeV, the energy of cesium ¹³⁷ Cs (dashed line) is 0.66 MeV, and the energy of both sources is about 2 There is a double difference. Therefore, the relationship between the number of pulses and the pulse height is as shown in FIG. However, cobalt ⁶⁰ Co is indicated by a dashed line, and cesium ¹³⁷ Cs is indicated by a broken line. And
Generating a pulse signal L of the light emitting diode 17, by adjusting the pulse height position shown in FIG. 11, cobalt ⁶⁰ C
When o is the source, the pulse signal from the source and the pulse signal from the light emitting diode 17 can be easily determined.

When the pulse signal L is at the peak position shown in FIG. 11, even if the source is cobalt ⁶⁰ Co, cesium
^{Even with 137} Cs, the pulse signal from the source and the pulse signal from the light emitting diode 17 can be easily distinguished. However, when the source is cesium ¹³⁷ Cs, the use efficiency of the dynamic range of the amplifier 10 is low. Therefore, in the present invention, the excitation current of the light emitting diode 17 can be adjusted. If the excitation current is reduced to about 、 and the gain of the amplifier 10 is increased to about twice, the peak position of the signal L can be adjusted as shown in FIG. Of the amplifier 10 to improve the dynamic range usage efficiency of the amplifier 10.

FIG. 12 is a schematic structural view of another embodiment of the present invention, which is an example of a gamma ray measuring device having an explosion-proof structure. In FIG. 12, the detector 7 has a detector case 22 for accommodating the plasticine 5, and a spacer 23 is attached to the upper portion of the plasticine 5 for fixing and for absorbing the thermal expansion of the plasticine 5. is there. The lower part of the plasticine 5
It is fixed by the flange 24 of the detection unit case 22. An optical signal amplifying unit 25 is provided below the detecting unit case 22. The optical signal amplifying unit 25 includes an amplifying unit case 26 and a photomultiplier tube 6.
Are enclosed by a base 27 for mounting the same. The base 27 has two glass light paths through which light passes, and a glass 28 through which the plastic light and the light-emitting diode light enter the photomultiplier tube 6 through the glass from the plasticine 5 and a light signal amplifying unit 25. There is a glass 29 for entering the detection unit case 22 from the side. A reflection plate 30 is mounted inside the detection unit case 22 so that the light-emitting diode light can efficiently enter the plasticine 5.

On the lower side of the amplifying section case 26, a terminal block 31 for transmitting and receiving electric signals to and from the outside and for supplying power is provided.
There is. Reference numeral 32 denotes a terminal box cover,
Screwed into. 33 screw holes.
Is fitted with a pipe for protecting an electric wire introduced from the outside. As described above, the amplification unit case 26 and the base 2
7, glass 28, glass 29, and terminal box cover 32 have an explosion-proof structure so that they can be used even in a combustible atmosphere. The glass 28 is fixed to the base 27 by a glass retainer 34, and the photomultiplier tube 6 is fixed by the photomultiplier tube holder 35 and the spring 36 so that the glass 28 and the light receiving surface of the photomultiplier tube 6 are in close contact. , Is always pressed against the glass 28.

The interface between the plastic 5, the glass 28 and the photomultiplier 6 is coated with silicon oil or grease having a low vapor pressure in order to improve the light transmission. Further, the glass 29 is fixed to the base 27 by the light emitting diode holder 37. A light-emitting diode holder 37 fixed by the base 27 is disposed close to the glass 29. The glass 29 may be provided with a means for adjusting the light amount of the light emitting diode 17 so as to form an aperture or add fogging.

The photomultiplier 6 is supplied with a high voltage from a high voltage power supply 15 and is operated. The high-voltage power supply 15 is operated by a signal from the HV control circuit 16 on the printed circuit board 21. The light emitting diode 17 emits light when a pulse signal is supplied from a pulse oscillator 18 and a temperature compensation circuit 19 (not shown in FIG. 10) on the printed circuit board 21. The detection unit case 22 and the amplification unit case 26 are connected by screws 38. In the example of FIG. 12, since the light emitting diode 17 has an explosion proof structure, the light emitting diode 17 is installed on the amplification unit case 26 side. However, if the explosion proof structure is unnecessary, the light emitting diode 17 is directly installed on the detection unit case 22. Sometimes.

Since the gamma ray detector is often installed outdoors, it is sealed with an O-ring 39 so that rainwater and dust do not enter inside. further,
A desiccant 40 such as silica gel and an oxygen scavenger (for example, a substance such as iron powder) are contained in the detection unit case 22.
The incidence of light and the change of the reflection performance due to the dew condensation on the surface of the plasticine 5 do not occur. Further, with the oxygen scavenger, it is possible to prevent the deterioration of the translucency due to the yellowing of the plasticine 5 due to oxygen, and to suppress the change with time. Deterioration due to oxygen varies depending on the ambient temperature.
At 50 degrees C per year, it reaches -5% / year. In the example of FIG. 12, the same effect as in the example of FIG. 1 can be obtained. Although the example of FIG. 12 is a case of a gamma ray level meter, by shortening the length of the plasticine 5 to 50 to 300 mm, the structure can be used as it is as a density meter or a level switch.

FIG. 13 is a schematic diagram showing a main part of still another embodiment of the present invention. In the example of FIG. 13, FIG.
Of the operation unit 14 in the example of FIG.
It is configured to be executed by U42. That is, the output signal of the comparator 13 is supplied to the MPU 42, and the MPU 42 performs an operation for HV control. Then, a signal indicating a result calculated by the MPU 42 is supplied to the HV control circuit 16. The HV control circuit 16 controls the high-voltage power supply 15 according to the supplied signal, and controls the voltage supplied to the photomultiplier tube 6. The output signal from the arithmetic unit 12 is supplied to the output circuit 43 via the MPU 42. The output signal of the output circuit 43 is supplied to a host control system or the like.

In the example of FIG. 13, the same effect as in the example of FIG. 1 can be obtained. In the example of FIG. 13, the number of external connection cables is increased by two pairs as compared with the examples of FIGS. 1 and 12.
4, the printed circuit board 21 can be significantly reduced in size. Furthermore, if an operation abnormality occurs in the amplifier 10 or the like from the light emitting diode signal supplied to the converter 41, this can be detected.

By the way, the gamma ray measuring device is often installed in a flammable atmosphere, in a high temperature state, in dust, or in a place where humans cannot approach. For this reason, it is necessary to detect the surrounding state of the gamma ray measuring device. One of the ambient conditions is the ambient temperature. FIG. 14 is a schematic configuration diagram of still another embodiment of the present invention, in which an ambient temperature state is also detected. The difference between the example of FIG. 14 and the example of FIG. 1 is that a light emitting diode 17A, a flip-flop circuit (pulse signal dividing means) 18A, an amplifier 19A, a comparator 11A, and a calculator 12A are added. By the way, other configurations are the same. In FIG. 14, a pulse signal generated from a pulse oscillator 18 is supplied to a flip-flop circuit 18A to form two types of pulse signals in which pulse generation timing is alternated. Then, one pulse signal is supplied to the light emitting diode 17 via the temperature compensation circuit 19. The other pulse signal from the flip-flop circuit 18A is supplied to the amplifier 19A, and after being amplified, is supplied to the light emitting diode 17A. Light emitting diode 17A
Is for detecting the ambient temperature, and is disposed near the light emitting diode 17. Since the light emitting diode 17A is not temperature-compensated, the light emission amount changes depending on the ambient temperature.

The signal from the photomultiplier tube 6 is supplied to an amplifier 10
Is supplied to the time constant circuit 20, the comparator 11, and the comparator 11A. The signal from the light emitting diode 17A is selected by the comparator 11A and supplied to the arithmetic unit 12A. Then, the ambient temperature is calculated by the calculator 12A. Then, a signal corresponding to the ambient temperature is supplied from the arithmetic unit 12A to the converter. In the example shown in FIG. 14, the same effects as those in the example shown in FIG. 1 can be obtained, and the ambient temperature can be detected.

FIG. 15 is a schematic configuration diagram of still another embodiment of the present invention, in which an ambient temperature state is detected similarly to the example of FIG. The difference between the example of FIG. 15 and the example of FIG. 14 is that the amplifier 19A is omitted.
Here, a light emitting diode 17B having a light emitting wavelength (for example, red) different from the light emitting wavelength (for example, blue) of the light emitting diode 17 is provided. If the light emitting wavelength of the light emitting diode is different, the gain of the photomultiplier tube 6 is different. This is equivalent to the difference between the light emission amounts of the light emitting diodes 17 and 17B. In the example of FIG. 15, the same effect as in the example of FIG. 14 can be obtained by omitting the amplifier 19A.

In the example shown in FIG. 15, it is possible to use a light emitting diode having a light emission amount different from that of the diode 17 even if a pulse signal of the same crest level is supplied instead of the light emitting diode 17B. In addition, the light emitting diodes 17 and 17B may be light emitting means having two light emitting elements that emit different amounts of light. In the illustrated example, the light emitting diode is used as the reference light generating means. However, any light emitting element other than the light emitting diode may be used as long as the light emitting pulse height, the light emitting pulse width, and the number of light emitting pulses can be adjusted.

[0042]

Since the present invention is configured as described above, it has the following effects. A gamma source,
A gamma ray measuring device having a rod-shaped plastic scintillator and photoelectric conversion means for receiving an optical signal, and measuring a change in the level or density of an object to be measured by a pulse count rate of an output pulse signal of the photoelectric conversion means. , A pulse signal generator having an adjustable output pulse width, and an optical pulse signal having a pulse width different from the pulse width of the pulse signal generated from the gamma ray source is generated based on the pulse signal from the pulse signal generator. Reference light generating means, and temperature compensating means for making the light emission amount of the light pulse signal generated from the reference light generating means a substantially constant amount regardless of a change in ambient temperature,
Voltage control means for changing the supply voltage to the photoelectric conversion means so that the number of pulses from the reference light generation means supplied via the photoelectric conversion means has a predetermined value.
Thus, it is possible to realize a gamma ray measuring device that is less affected by the change in ambient temperature and statistical noise, is easier to manage, and has improved measurement accuracy. Further, since the gamma ray source and the reference light generating means have different pulse widths from each other, the pulse signals can be easily separated, and the gamma ray source can have a wide dynamic range. Therefore, a gamma ray measuring device that can support various types of gamma ray sources is realized.

Further, the apparatus has a gamma ray source, a rod-shaped plastic scintillator, and photoelectric conversion means for receiving an optical signal. The level and density of an object to be measured are determined by the pulse count rate of the output pulse signal of the photoelectric conversion means. In a gamma ray measuring device for measuring a change in the pulse signal, a pulse signal generating means capable of adjusting a peak level of an output pulse signal, and a pulse signal generated from a gamma ray source based on a pulse signal from the pulse signal generating section. A reference light generating means for generating light pulse signals of different peak levels, a temperature compensating means for making the amount of light of the light pulse signal generated from the reference light generating means substantially constant irrespective of a change in ambient temperature; Supply to the photoelectric conversion means such that the number of pulses of the pulse signal from the reference light generation means, which is supplied through the electrical conversion means, becomes a predetermined value. Comprising a voltage control means for varying the pressure, the. Thus, it is possible to realize a gamma ray measuring device that is less affected by the change in ambient temperature and statistical noise, is easier to manage, and has improved measurement accuracy. Further, since the peak level of the output pulse signal, that is, the peak level of the optical pulse signal generated by the reference light generating means is adjustable, the gamma ray source and the reference light generating means are different from each other, Separation of the pulse signal is easy, and the dynamic range of the gamma ray source can be widened. Therefore, a gamma ray measuring device that can support various types of gamma ray sources is realized.

Further, the apparatus has a gamma ray source, a rod-shaped plastic scintillator, and photoelectric conversion means for receiving an optical signal. The level and density of the object to be measured are determined by the pulse count rate of the output pulse signal of the photoelectric conversion means. In a gamma ray measuring device for measuring changes such as, a pulse signal generating means having a constant number of output pulses, a reference light generating means for generating a light pulse signal of a predetermined number of pulses, and an optical pulse generated from the reference light generating means Temperature compensation means for making the light emission amount of the signal substantially constant regardless of changes in the ambient temperature, and the number of pulses of the pulse signal from the reference light generation means, which is supplied via the photoelectric conversion means, has a predetermined value. Voltage control means for changing a supply voltage to the photoelectric conversion means. Thus, it is possible to realize a gamma ray measuring device that is less affected by the change in ambient temperature and statistical noise, is easier to manage, and has improved measurement accuracy. Further, since the reference light generation means has a constant number of light pulse signals generated, voltage control based on the light pulse signal from the reference light generation means can be performed in a short time, and the measurement speed has been improved. A gamma ray measuring device is realized.

According to a configuration in which, in addition to the temperature-compensated reference light generating means, a light generating means whose amount of generated light changes due to a change in the ambient temperature is provided, a gamma ray measuring device capable of detecting the ambient temperature is realized. You can do it.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of an example of a temperature compensation circuit.

FIG. 3 is a circuit diagram of another example of the temperature compensation circuit.

FIG. 4 is a diagram showing a relationship between a current supplied to a light emitting diode and an output signal of a photomultiplier tube.

FIG. 5 is a diagram illustrating a relationship between a pulse signal supplied to a light emitting diode and an output signal of a photomultiplier tube.

FIG. 6 is a diagram illustrating a relationship between the number of pulses and a pulse height when a pulse width of a pulse signal supplied to a light emitting diode is 20 μs.

FIG. 7 is a diagram illustrating a relationship between the number of pulses and a pulse height when a pulse width of a pulse signal supplied to a light emitting diode is 2 μs.

FIG. 8 is a diagram illustrating a relationship between the number of pulses of a signal supplied to a time constant circuit and a pulse height;

FIG. 9 is a diagram illustrating a relationship between the number of pulses of a signal output from a time constant circuit and a pulse height;

FIG. 10 is a diagram for explaining statistical noise of an α-ray source.

FIG. 11 is a diagram for explaining that a light emitting pulse height of a light emitting diode is adjustable.

FIG. 12 is a schematic configuration diagram of another embodiment of the present invention.

FIG. 13 is a schematic diagram of a main part of still another embodiment of the present invention.

FIG. 14 is a schematic configuration diagram of still another embodiment of the present invention.

FIG. 15 is a schematic configuration diagram of still another embodiment of the present invention.

FIG. 16 is a schematic configuration diagram of an example of a conventional gamma ray measuring device.

17 is a diagram showing a relationship between the number of pulses of a signal from the photomultiplier tube and a pulse height in the example of FIG. 16;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container 2 Liquid 3 Radiation source container 4 Gamma ray source 5 Plastic scintillator 6 Photomultiplier tube 7 Detector 8 Light guide 9 Light pulser 10, 19A Amplifier 11, 11A, 13 Comparator 12, 12A, 14 Operation unit 15 High voltage power supply 16 HV control Circuit 17, 17A, 17B Light emitting diode 18 Pulse oscillator 18A Flip-flop circuit 19 Temperature compensation circuit 20 Time constant circuit 41 Converter 42 MPU 43 Output circuit

Claims (12)

(57) [Claims] 1. A gamma ray source disposed on one side of a measurement container, a rod-shaped plastic scintillator disposed at a position facing the gamma ray source with the measurement container interposed therebetween, and directly connected to one end of the rod-shaped plastic scintillator. Or a photoelectric conversion means for receiving an optical signal through a light guide, and the level or density of the object to be measured in the measurement container is changed by the pulse count rate of the output pulse signal of the photoelectric conversion means. A gamma ray measuring device for measuring the pulse signal, wherein a pulse signal generating means capable of adjusting an output pulse width; and a pulse signal from the pulse signal generating means,
A reference light generating means for generating an optical pulse signal having a pulse width different from the pulse width of the pulse signal generated from the gamma ray source; and a wave height of the pulse signal generated from the pulse signal generating means according to a change in ambient temperature. Temperature compensating means for causing the light emission amount of the optical pulse signal generated from the reference light generating means to be substantially constant irrespective of a change in ambient temperature; and the reference supplied through the photoelectric conversion means. A gamma ray measuring device, comprising: voltage control means for changing a supply voltage to the photoelectric conversion means so that the number of pulses of the pulse signal from the light generation means has a predetermined value. 2. A gamma ray source disposed on one side of a measurement container, a rod-shaped plastic scintillator disposed at a position facing the gamma ray source with the measurement container interposed therebetween, and directly connected to one end of the rod-shaped plastic scintillator. Or a photoelectric conversion means for receiving an optical signal through a light guide, and the level or density of the object to be measured in the measurement container is changed by the pulse count rate of the output pulse signal of the photoelectric conversion means. In a gamma ray measuring device for measuring the pulse signal, a pulse signal generating means capable of adjusting the peak level of the output pulse signal, and based on the pulse signal from the pulse signal generating means,
A reference light generating means for generating a light pulse signal having a crest level different from the crest level of the pulse signal generated from the gamma ray source; and a crest of the pulse signal generated from the pulse signal generating means according to a change in ambient temperature. Temperature compensating means for causing the light emission amount of the optical pulse signal generated from the reference light generating means to be substantially constant irrespective of a change in the ambient temperature, and supplied through the photoelectric conversion means. A gamma ray measuring device, comprising: voltage control means for changing a supply voltage to the photoelectric conversion means so that the number of pulses of the pulse signal from the reference light generation means has a predetermined value. 3. A gamma ray source disposed on one side of a measurement container, a rod-shaped plastic scintillator disposed at a position facing the gamma ray source with the measurement container interposed therebetween, and directly connected to one end of the rod-shaped plastic scintillator. Or a photoelectric conversion means for receiving an optical signal through a light guide, and the level or density of the object to be measured in the measurement container is changed by the pulse count rate of the output pulse signal of the photoelectric conversion means. In a gamma ray measuring device for measuring the pulse signal, a pulse signal generating means having a constant output pulse number, and a pulse signal from the pulse signal generating means,
A reference light generating means for generating an optical pulse signal having a predetermined number of pulses; and a wave height of the pulse signal generated from the pulse signal generating means is changed in accordance with a change in ambient temperature, and the reference light generating means generates the pulse height. Temperature compensating means for making the amount of emitted light pulse signal substantially constant regardless of changes in the ambient temperature; and the number of pulses of the pulse signal from the reference light generating means supplied through the photoelectric conversion means And a voltage control means for changing a supply voltage to the photoelectric conversion means so that the value of the photoelectric conversion means becomes a predetermined value. 4. The gamma ray measuring device according to claim 1, wherein the reference light generating means is a light emitting diode, and a pulse width of a pulse signal supplied to the light emitting diode. Is 1 to 10 μs. 5. The gamma ray measuring device according to claim 1, wherein the reference light generating means is a light emitting diode, and the light emitting diode has an emission wavelength of 400 to 600 nm. A gamma ray measuring device, characterized in that: 6. The gamma ray measuring device according to claim 1, wherein the reference light emitting unit is a light emitting diode, and the reference light emitting unit is connected to the reference light emitting unit via the photoelectric conversion unit. A gamma ray measuring device, wherein a count rate of a generated pulse signal is 0.5% to 10% of a count rate of a pulse signal generated from a gamma ray through the photoelectric conversion means. 7. The gamma ray measuring device according to claim 1, wherein an amplifier for amplifying a signal from said photoelectric conversion means , and a gamma ray source from an output signal from said amplifier. Trust based on
A first comparator for extracting a signal, and a signal extracted by the first comparator.
A first calculator for calculating the level and density of the device under test, and a signal based on a gamma ray source from an output signal from the amplifier.
Time constant for separating the signal from the signal based on the reference light generation means.
And road, from the output signal from the time constant circuit, a reference light generation means
A second comparator for extracting a signal based on the number of pulses of the signal extracted by the second comparator;
Calculates the difference between the above pulse number and the specified number by comparing with the specified number
And a high-voltage power supply for supplying a high voltage to the photoelectric conversion unit, wherein the voltage control unit outputs the second operation unit.
A gamma ray measuring device characterized by changing an output voltage of a high voltage power supply according to a force signal . 8. The gamma ray measuring device according to claim 7 , wherein MV is a control signal , PB is a proportional band, and Pin is a second control signal .
The number of pulses of the output signal of the parator, Pr, is used as a reference light generating means.
From the total number of generated pulses, PS is the reference ratio between Pin and Pr,
If Ti is the integration time, the second computing unit calculates MV = (1
/ PB) (PS- (Pin / Pr)) / (Ti + 1)
The control signal MV is controlled by the voltage control described above.
A gamma ray measuring device for supplying to a control means . 9. The gamma ray measuring device according to claim 1, wherein the reference light generating means comprises:
A light emitting diode, the light emitting diode
In the package, two light emitting dies with different emission wavelengths
A gamma ray measuring device characterized by incorporating an auto diode . 10. The gamma ray measuring device according to claim 9 , wherein:
Two types of patterns in which the pulse signal generation timing is alternated
Pulse signal dividing means for generating a pulse signal.
In addition, the two light emitting diode elements are combined with the two types of light emitting diodes.
A gamma ray measuring device to which a loose signal is supplied and light is emitted substantially alternately . 11. The gamma ray measuring device according to claim 8, wherein the ratio Pin / Pr is 0.02 ≦ Pin / Pr ≦ 0.2.
A gamma ray measuring device , wherein 0.8 ≦ Pin / Pr ≦ 0.98 . 12. The gamma-ray measurement apparatus any one <br/> according one of claims 1, 2, 3, at least, photoelectrochemical
Conversion means, pulse signal generation means, temperature compensation means,
The voltage control means and the reference light generating means are
The explosion-proof case is housed in a case.
It is connected to a stick scintillator, and two
A gamma ray measuring device , wherein independent light paths are formed at different places .